Kathleen Bridges, School of Plant, Environmental, and Soil Sciences, Louisiana State University, Baton Rouge, LA, Lisa M. Fultz, School of Plant, Environmental & Soil Science, LSU Agricultural Center - Baton Rouge, Baton Rouge, LA, Josh Lofton, Plant and Soil Science, Oklahoma State University, Stillwater, OK, Beatrix J. Haggard, Oklahoma State University, Stillwater, OK and Wink Alison, Louisiana State University Northeast Research & Ext. Ctr., Winnsboro, LA
With increasing production costs and concerns for soil health, it is no longer sustainable for producers to rely solely on frequent high rate fertilizer applications. One potential alternative is incorporation of a diverse mixture of annual grasses, clovers, and crucifer species over-seeded into a long-term commercial grazing operation. Soil physical, chemical, and biological properties were assessed from soils collected immediately prior to planting. Samples were collected across a topographic sequence (summit, backslope and footslope) to a depth of 30cm at 7.5cm intervals. Three samples per location were collected from the summit and along four directional slope faces (north, east, west, and southwest). Soil chemical assessments included macronutrients, pH, soil organic matter (SOM), soil organic C (SOC), and total nitrogen (TN) to 30cm. Microbial community structure (fatty acid profiles) and enzyme activity assays were conducted on samples collected to 15 cm. Depth was most influential for total microbial biomass, SOC, and TN, which were highest at 0-7.5cm. Saprophytic fungi were found in greater relative abundance at 7.5-15cm depth. However, soil depth had no significant effect on relative abundance of arbuscular mycorrhizal fungi which were highest on the backslope of the eastern slope. Topography had a significant influence on total microbial biomass, SOC, TN, and K with greatest concentrations at the summit. Depth and location had an interactive effect on NO3--N which was found in greatest concentration in the 0-7.5cm layer of the northern slope. The highest measurements for SOM and P were at 0-7.5cm depth of the north facing footslope and for NH4+-N, the 0-7.5 depth of the west facing backslope. These differences in soil chemical and biological properties may drive or be driven by the emergence of observed vegetation communities.